Replying to Signatures bitches

so i since i have been on newschoolers i have always read peoples signatures thinking they were part of their (usualy shitty) posts. but my other computer is in the shop, so im using my laptop. my desktop is running windows XP and i use firefox 2. on my laptop im using Linux, with Firefox. and when im on this website with this computer, all the signatures are light grey and are distinquished from the rest of the post. why is it like this on this computer and not my other one?